MUSEUM OF COMPARATIVE ZOOLOGY. 437 



pose of answering three questions which were left by Biitschli in an 

 unsatisfactory condition : (1.) how the germinative vesicle transforms 

 itself into the nuclear spindle ; (2.) whether the fecundation is of in- 

 fluence on the origin of the nuclear spindle and the polar globules ; and 

 (3.) whether the nucleus (germinative vesicle) is completely eliminated, 

 or is partly retained and passes into the segmentation nuclei. 



The ovarian eggs of Hsemopis contain a comparatively small germi- 

 native vesicle with membrane in which are found a single nucleolus and 

 accessory nucleoli ; the latter are stained deeply in osmic acid and 

 carmine. For this reason they are both to be considered nuclear sub- 

 stance. At maturity the nucleolus divides, and the nuclear membrane 

 dissolves so that there remains in the egg only a clear spot destitute of 

 granules in which parts of the stained nucleolus are observable. One 

 finds in place of this a spindle, which is variously situated, either near 

 the centre of the yolk, or more to one side, and then often with its axis 

 radially placed, one end being at the surface. When centrally located 

 it is surrounded by the same clear area which surrounds the fragments 

 of the nucleolus at an earlier stage. The fibres of the spindle converge 

 in two points, which are sharply expressed in Hertwig's drawings; they 

 are formed, he says, of compacted nuclear substance, which takes the form 

 of a single dark nucleus (Kern) or several such. This is surrounded by 

 a clear area of protoplasm, around which the yolk granules have a radial 

 arrangement. The middle aone of thickenings becomes especially prom- 

 inent when the egg is treated with reagents. Hertwig considers as 

 stages in the process of the formation of the spindle, (1.) a condition in 

 which there are in the middle of the egg two homogeneous areas close 

 together, around which the yolk granules are arranged in rays, — there 

 being between these two systems a number of dark, coagulated, irregu- 

 larly formed corpuscles, which have the appearance of nuclear substance ; 

 and (2.) a condition in which there is found in place of these corpuscles 

 an indistinctly limited structure of approximately spindle shape, in the 

 middle of which are found small condensed granules not yet arranged 

 into a regular granular disk. 



From these observations he finds reason to dissent from Biitschli's 

 view that the spindle is the entire germinative vesicle metamorphosed. 

 He disagrees because of the great difference in the size of these two forms 

 of the nucleus ; the absence of a distinct membrane about the spindle ; 

 and the condition of the egg, so often met with, in which the germina- 

 tive dot or its fragments were the only parts of the vesicle that were 

 preserved. Hertwig does not deny a genetic connection between the 



